The invention relates to a printing apparatus and process pursuant to which a light sensitive material such as color print paper is exposed to primary color lights, red, green and blue, through flats to simulate the desired printing ink colors of cyan, magenta and yellow. More specifically the invention is directed to an apparatus in which a single light sensitive material is exposed to the three primary colors through flats or films to obtain a composite color layout for proofing purposes so that the various positions and content of color produced by the flats can be proofed to be sure that an accurate composite color layout will be created from the flats.
Proofing of colors is a long established practice in the graphic arts industry. The printer wants to be sure that the final layout will have the correct shades of color in the correct location before exposing individual printing plates through the flats and running the job on a printing press. This proofing procedure has been very complex in the past. Prior art systems have conventionally used a large number of exposures. Past procedures have sequentially passed a red, green and blue filter past a single lamp or light source. Since various shades of cyan, magenta and yellow require contamination of the primary complementary color with the other colors, a typical procedure used in the past has been to expose the material through all three flats, sequentially using as many as three primary colors for each flat, thus requiring nine or more exposures for the position proof.
Naturally, the more light which is used to make each exposure requires closer and closer control of the specific time and intensity of each successive exposure. Also the spectral sensitivity of the emulsion is typically such that exposure through any one flat may lead to unwanted contamination of the color because of the overlap.
In addition, it is extremely difficult to maintain a uniform intensity of the light in that the intensity of lamps change as the light gets hotter or ages or the like. To add the black exposures, exposures for fold and cut lines and an additional exposure for background color increases the complexity and complicates the acceptability of the final position and color acceptance proof.